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Tuesday, December 3, 2013

Carriers Move to Limit Public Safety Cellular Data Transfer

A customer of ours told us, and this has not yet been confirmed, that Verizon is moving to follow the T-Mobile model of cellular data transfer throttling for public safety. Basically you will pay for a 5GB transfer cap at full LTE 4G speed (measured in Mbps) at a fixed fee, then once you hit the cap you can still transfer but your speed will be reduced to 256kbps or less. I assume that you can still purchase a plan with a higher transfer cap, but it will cost you more.

Actually I use T-Mobile 4G with such a plan for my cell phone and it is a great deal. But then I am only surfing the net, checking my emails and checking in on Facebook.

For police and other public safety personnel who have become accustomed to unlimited transfer at full speed, this presents a big problem. Many of our folks in blue use IP cameras to stream video from a remote site over cellular. It is easy to install, it is available everywhere, and it is compact.

Unfortunately streaming video requires a lot of bandwidth. A typical 720p at 15fps camera will use about 1.7Mbps. That is about 13MB per minute, or 765MB per hour. So you can easily reach your 5GB transfer limit in about 6 1/2 hours. So if you need 24x7 streaming you have to compromise.

Many IP cameras support multiple streams for the same video and some have SD cards that allow up to 64GB of storage (83 hours of 720p at 15fps). So you can send one small stream over cellular at a low resolution and slow frame rate while storing locally. If you were willing to run at VGA resolution (640x480) at 4fps you could get an video stream for "situational awareness" in 150kbps. But that is not a very good image quality, it is slow and jerky, and it still will burn through your data plan at 1MB per minute, or 1.6GB per day. So you could run for about 3 days a month before you run out of data transfer on your plan.

Another issue with this strategy is that you will need to determine what the minimum data rate that your cellular link supports is. If you are in an area with only 3G and are on the fringe of the coverage area or in an area that is highly congested, you may only achieve 100kbps. So you need to set your camera at this low rate in order to assure that your stream gets across. Your camera cannot adapt.

And then you have to think about retrieving your video evidence from your camera. You have your cellular connection, but if you try to transfer the locally stored high quality video from the camera back over that cell connection, you are again faced with your data cap.

And what if you want a 1080p camera or a 5MP camera, or a 20MP camera, or faster frame rate. What will you do?